Effects of Mg2+ on Ca2+ handling by the sarcoplasmic reticulum in skinned skeletal and cardiac muscle fibres

1994 ◽  
Vol 428 (3-4) ◽  
pp. 331-339 ◽  
Author(s):  
A. A. Kabbara ◽  
D. G. Stephenson
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Muscle Fibres

scholarly journals Caffeine and micromolar Ca2+ concentrations can release Ca2+ from ryanodine-sensitive stores in crab and lobster striated muscle fibres

1996 ◽  
Vol 199 (11) ◽  
pp. 2419-2428 ◽  
Author(s):  
T Lea
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Striated Muscle ◽  
Abdominal Muscle ◽  
Isometric Tension ◽  
Muscle Fibres ◽  
Phasic Contraction ◽  
Crustacean Muscle ◽  
Time Integral ◽  
Variable Nature

Ca2+ release mechanisms were studied in striated muscle from the walking legs of crabs using isometric tension recordings from isolated myofibrillar bundles. Caffeine-induced phasic contractions had properties consistent with Ca2+ release from a sarcoplasmic store, which could be optimally loaded in the presence of ATP at pCa 6.4­6.1. Ryanodine (10 µmol l-1) abolished the caffeine-induced contractions and in solutions with low Ca2+ buffering (0.1 mmol l-1 EGTA) itself caused phasic contractions, indicative of Ca2+ release. Ca2+-induced Ca2+ release (CICR) was observed in a pCa 5.8 solution (buffered by 1 mmol l-1 EGTA) as a phasic contraction of variable nature, inhibited by ryanodine (10 µmol l-1), procaine (10 mmol l-1) or benzocaine (5 mmol l-1). Ca2+ release was measured as a function of releasing pCa by using the force­time integral of the caffeine-induced contraction as an estimate of the Ca2+ remaining in the store. After the Ca2+ store had been loaded for 2 min at pCa 6.6, CICR was measured in the presence of 1 mmol l-1 Mg2+, 1 mmol l-1 EGTA and 5 mmol l-1 ATP. The threshold pCa for CICR was 6.0­6.4 under these conditions and more than 90 % of stored Ca2+ was released in 1 min by pCa values in the range 3.5­5.3. Benzocaine totally inhibited the release and promoted extra Ca2+ loading. Preliminary experiments showed a similar caffeine-releasable store in lobster abdominal muscle, which was slightly less sensitive to free [Ca2+]. It is concluded that in crustacean muscle caffeine and micromolar [Ca2+] can release Ca2+ from a ryanodine-sensitive store, which in many respects is similar to the sarcoplasmic reticulum of vertebrate skeletal and cardiac muscle.

The transverse tubular (T) system of rat cardiac muscle fibers as demonstrated by tannic acid mordanting

1978 ◽  
Vol 56 (9) ◽  
pp. 1906-1916 ◽  
Author(s):  
T. S. Leeson
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Tannic Acid ◽  
Extracellular Space ◽  
Inverse Relationship ◽  
Muscle Fibres ◽  
Fiber Size ◽  
T Tubules ◽  
Cardiac Muscle Fibers ◽  
T System

T-tubules and subsarcolemmal caveolae in rat cardiac muscle fibres have been studied using the tannic acid mordanting technique. While T-tubules form an extensive and relatively regular meshwork with triads at Z-lines in ventricular fibers, in atrial fibers the tubules are often absent, or very sparse and with an irregular distribution. There appears to be a relation to fiber size, the meshwork being more extensive in fibers of larger diameter, and an inverse relationship to the number of couplings found between sarcoplasmic reticulum and plasmalemma. In larger atrial fibers, while the T-tubule meshwork was extensive, it did not show the regularity of distribution found in ventricular fibers. T-tubule continuity with the extracellular space was visualized clearly, both directly and indirectly via subsarcolemmal caveolae.

Anchorfibers and the Topography of Junctional SR

1977 ◽  
Vol 35 ◽  
pp. 582-583
Author(s):  
James Junker ◽  
Joachim R. Sommer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Single Filament ◽  
Relaxation Cycle ◽  
10 Nm Filaments ◽  
Junctional Sarcoplasmic Reticulum

Junctional sarcoplasmic reticulum (JSR) in all its forms (extended JSR, JSR of couplings, corbular SR) in both skeletal and cardiac muscle is always located at the Z - I regions of the sarcomeres. The Z tubule is a tubule of the free SR (non-specialized SR) which is consistently located at the Z lines in cardiac muscle (1). Short connections between JSR and Z lines have been described (2), and bundles of filaments at Z lines have been seen in skeletal (3) and cardiac (4) muscle. In opossum cardiac muscle, we have seen bundles of 10 nm filaments stretching across interfibrillary spaces and adjacent myofibrils with extensions to the plasma- lemma in longitudinal (Fig. 1) and transverse (Fig. 2) sections. Only an occasional single filament is seen elsewhere along a sarcomere. We propose that these filaments represent anchor fibers that maintain the observed invariant topography of the free SR and JSR throughout the contraction-relaxation cycle.

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